[Beowulf] Airflow

[Mark Hahn]

> How much harm does removing the computer case do?

in principle, none at all.

> I know computer cases are 
> designed for the air flow,

hah!
depends on the kind of case.  it might be neat to run racks of 1u's 
without case - essentially bladizing them.  the density would be high 
enough to avoid questions of where the air is actually flowing.

for 3-4U and bigger, there's quite a lot of space, and IMO, it could
be risky to remove the case (mainly because you loose control of the 
intake and/or outflow.

but the airflow in lots of minitower-type desktops is confused enough
that I wouldn't worry too much about it.  if you have a low-density cluster 
of minitowers on wire racks, I'd worry more about whole-room airflow.
obviously, you want to maximize the good done by whatever airflow you have.
if you have minitowers, packing them together tightly (sides and top/bottom)
will create a wall that will avoid useless airflow.  blanking panels on 
rackmounted systems are similarly good.

> heating problems. My air conditioner will be enough for the amount of heat 
> generated, but will I need circulation fans in the room also?

you certainly do need good overall circulation.  I'm always astounded 
when I see a machineroom which has non-raised floors, multiple rows 
of machines, and a single front-intake-front-outflow chiller.  such 
rooms usually have the machine rows front-to-back (no hot/cold aisles.)
such an organization ("the accidental machineroom") can probably handle 
at most a couple KW per rack versus >10K for something more intentional...

> I created a test cluster of 8 nodes, removing all the cases and mounting 
> everything onto a wire rack. It works fine with no heat problems. But I am 
> concerned that once I build the entire 100 node cluster there will be 
> problems. The book I am reading on HPC does not go into that detail.

sounds like minitower cases, right?  as long as you have some kind of 
consistent circulation plan, you certainly don't need full cases.

> I was thinking an air purifier that is always on will slowly circulate the 
> air when the air conditioner is off.

why would the chiller be off?  you do need to keep the air circulating
unless you have quite low overall power and power-density.

> I just don't have enough room to build this with the computers still in 
> cases.

cases don't have to be big, and the bigger ones tend to have more 
haphazard airflow designs...